While Helicobacter pylori is now established as a pivotal factor in gastric carcinogenesis, its mechanisms of action and timing in the premalignant process are the subject of research. This project builds upon a recently completed 6-year randomized chemoprevention trial in a high-risk region of Colombia. A significantly greater regression of premalignant lesions was observed in study participants who were treated and were cleared of H. pylori infection. Upon completion of the trial, participants who had not been in the anti-H. pylori treatment arm were offered standard triple therapy. Quarterly contact has been maintained with trial participants, and this project now proposes to evaluate the long-term effectiveness of anti-H. pylori treatment in an adult population in which the community prevalence of infection is greater than 90 percent. The specific aims of the study are to: 1. determine the proportion of subjects free of infection in 2002; 2. document the reinfection rates from 2002 to 2007 in subjects free of infection in 2002; 3. compare the H. pylori genotypes in persons receiving treatment and found to be free of infection during the follow-up phase with prior pre-treatment genotypes (1998); 4. determine the status of histopathologic lesions (progression; regression; no change) at the end of the follow-up phase (2006-7) in relation to their infection status over time and previous histopathology.